1. Field of the Invention
The present invention relates to a synthetic polymer hollow irregular multifilament yarn capable of being converted to a bulky yarn, a process and a spinneret for producing the same.
More particularly, the present invention relates to a synthetic polymer hollow irregular multifilament yarn in which each of the individual filaments is composed of three filamentary segments having a different longitudinal shrinking property, and as a whole, the longitudinal shrinking property of each individual filament varies along the longitudinal axis of the filament, and a process and a spinneret for producing the same.
2. Description of the Related Art
It is known that a synthetic polymer multifilament yarn capable of being converted to a bulky yarn by heating the yarn is obtained by blending two or more types of filaments each having a different heat shrinking property. This type of technology is disclosed, for instance, in U.S. Pat. No. 3,200,576 for S. B. Maerow et al.
When the above-mentioned type of blended multifilament yarn is heated, the filaments having a high heat shrinking property shrink at a high shrinkage, causing the remaining filaments having a low heat shrinking property to bulge from the high shrunk filaments and therefore, causing the yarn to become bulky.
In this type of the blended multifilament yarn, if the high shrinkage filaments have a larger denier than that of the low shrinkage filaments, the resultant bulky yarn usually exhibits a satisfactory rigidity and a soft touch.
As stated above, the multifilament yarn useful for producing a bulky yarn can be produced by blending at least two types of filaments each having a different shrinking property, for instance, in accordance with the process as disclosed in U.S. Pat. No. 4,153,660.
In the process of the U.S. patent, a number of undrawn filaments are produced by extruding a polymer melt through a spinneret having a number of spinning orifices. The resultant filaments are divided into two groups. A first finishing agent-containing aqueous liquid is applied to the first group of filaments and a second finishing agent-containing liquid having a higher boiling temperature than that of water is applied to the second group of filaments. The first and second groups of filaments are drawn separately at an elevated temperature under the same conditions. The first and second groups of the drawn filaments are then blended to provide a multifilament yarn.
The difference in the boiling temperatures of the first and second finishing agent-containing liquids results in a difference in the shrinking property of the first and second groups of drawn filaments. However, this process is disadvantageous in that a number of complicated procedures are necessary and two different finishing agents must be used.
In the melt-spinning process in which a plurality of filaments each having a different thickness are produced by using a single spinneret, the extruded filamentary streams are laterally oscillated and frequently adhere to each other, and thus, are sometimes broken. Therefore, in this process, it is very important to strictly control the draft applied to the filaments, and the amount, blowing rate, and direction of the cooling air applied to the filaments. This process is, therefore, complicated and inconvenient. U.S. Pat. Nos. 4,332,757 and 4,349,604 for L. E. Blackmon et al disclose a rather simple prcess for producing multifilament yarn capable of being converted to a bulky yarn without using complicated procedures.
In this process, a polymer melt is extruded through a pair of spinning orifices having extruding directions crossing each other at an angle, and extruding openings having different areas. A portion of the polymer melt is extruded through the large orifice at a lower extruding rate than that at which the remaining portion of the polymer melt is extruded through the small orifice. The resultant thin filamentary stream of the polymer melt extruded through the small orifice at a high extruding rate travels a sinuous path in a wave form and is combined with the resultant thick filamentary stream of the polymer melt extruded through the large orifice at a low extruding rate, which thick filamentary stream travels substantially straight. The resultant irregular filamentary stream is cool-solidified and is then taken up. This resultant irregular filament is composed of a thick filamentary segment which extends substantially straight and has a high shrinking property, and a thin filamentary segment sinuated in a wave form and combined to the thick filamentary segment and having a low shrinking property. The longitudinal shrinking property of the irregular filament varies along the length thereof.
The resultant multifilament yarns are converted to a woven or knitted fabric, and the fabric is then heat treated so that the multifilament yarns in the fabric are converted to bulky yarn. However, the heat-treated fabric, particularly the heat treated woven fabric consisting of the above-mentioned conventional irregular multifilament yarns, has an unsatisfactory bulkiness.
Usually, the above-mentioned type of conventional irregular filaments exhibit a relatively poor shrinking force when they are heated. Therefore, when the conventional irregular multifilament yarns are woven into a woven fabric, the heat-shrinkage of the individual filaments in the yarns is restricted by the weave structure. Therefore, the resultant heat-treated woven fabric exhibits an unsatisfactory bulkiness.
Also, when the above-mentioned conventional multifilament yarn is drawn, the difference in shrinking property between the thick straight filamentary segments and the thin sinuous filamentary segments tends to disappear. Accordingly, the conventional multifilament yarn must be used without being drawn. This necessity sometimes, causes the resultant bulky fabric to have an uneven shrinkage and/or dyeing property. Therefore, conditions adequate for dyeing and finishing the conventional irregular multifilament yarn fabrics are strictly limited.
Accordingly, the practical use of the above-mentioned irregular multifilament yarn is strictly restricted.